DESCRIPTION: Obesity continues to be a significant public health problem in America. While treatments for obesity are often successful in the short term, weight recidivism remains a critical problem. However, one of the factors strongly and consistently related to the maintenance of weight loss is exercise. In order to enhance the ability of exercise to facilitate weight maintenance, the mechanism must be elucidated. Exercise may have a direct effect on weight loss and maintenance by enhancing energy expenditure or indirect effects such as changing dietary fat preference, decreasing hunger, favorably modifying lean body mass and resting metabolic rate and improving psychological functioning. To date, the variable influence of exercise on all of these hypothesized mechanisms has never been simultaneously assessed. Thus, the primary aim of the proposed study is to assess the mechanism by which exercise facilitates weight maintenance. A sample of 250 to 300 women aged 25 to 45 and 30 to 50 pounds over ideal body weight will be recruited to participate in a 24 week behavioral weight loss program that includes diet and exercise. Subjects will be followed for 12 months post-treatment and measures related to exercise's hypothesized mechanisms of action will be assessed at 3 or 6 month intervals. Path analysis and structural equation modeling will be used to test the fit of various models depicting hypothesized relationships of exercise to weight maintenance. The proposed analysis allows for testing the relative contribution of direct and indirect effects of independent variables and additionally provides a vehicle for evaluating a number of theoretically correct mechanisms. The analysis will contribute a possible causal relationship between exercise and weight maintenance.